linux-kernel - Re: [PATCH v2 09/10] MIPS: i8042: Probe this device only if it exists

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Date:   Mon, 10 Jul 2017 17:07:17 +0200
From:   Jonas Gorski <jogo@...nwrt.org>
To:     Aleksandar Markovic <aleksandar.markovic@...rk.com>
Cc:     MIPS Mailing List <linux-mips@...ux-mips.org>,
        Miodrag Dinic <miodrag.dinic@...tec.com>,
        Goran Ferenc <goran.ferenc@...tec.com>,
        Aleksandar Markovic <aleksandar.markovic@...tec.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Douglas Leung <douglas.leung@...tec.com>,
        James Hogan <james.hogan@...tec.com>,
        linux-input@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Marcin Nowakowski <marcin.nowakowski@...tec.com>,
        Marcos Paulo de Souza <marcos.souza.org@...il.com>,
        Paul Burton <paul.burton@...tec.com>,
        Petar Jovanovic <petar.jovanovic@...tec.com>,
        Raghu Gandham <raghu.gandham@...tec.com>,
        Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [PATCH v2 09/10] MIPS: i8042: Probe this device only if it exists

Hi,

On 28 June 2017 at 17:47, Aleksandar Markovic
<aleksandar.markovic@...rk.com> wrote:
> From: Miodrag Dinic <miodrag.dinic@...tec.com>
>
> ARCH_MIGHT_HAVE_PC_SERIO is selected by default for MIPS platforms.
> As a consequence SERIO_I8042 would be automatically selected for any
> MIPS board which wants to enable input support like keyboard
> (INPUT_KEYBOARD) regardless of i8042 controller existence.
>
> The dependency is as follows :
>
> config ARCH_MIGHT_HAVE_PC_SERIO [=y]
>     Defined at drivers/input/serio/Kconfig:19
>     Depends on: !UML
>     Selected by: MIPS [=y]
>
> config SERIO
>     Defined at drivers/input/serio/Kconfig:4
>     default y
>     Depends on: !UML
>     Selected by: KEYBOARD_ATKBD [=y] && !UML && INPUT [=y] &&
>                  INPUT_KEYBOARD [=y]
>
> config SERIO_I8042
>     Defined at drivers/input/serio/Kconfig:28
>     tristate "i8042 PC Keyboard controller"
>     default y
>     Depends on: !UML && SERIO [=y] && ARCH_MIGHT_HAVE_PC_SERIO [=y]
>     Selected by: KEYBOARD_ATKBD [=y] && !UML && INPUT [=y] &&
>                  INPUT_KEYBOARD [=y] && ARCH_MIGHT_HAVE_PC_SERIO [=y]
>
> If this driver probes the I8042_DATA_REG not knowing if the device
> exists it can cause a kernel to crash. Using check_legacy_ioport()
> interface we can selectively enable this driver only for the MIPS
> boards which actually have the i8042 controller.
>
> New "Ranchu" virtual platform does not support i8042 controller
> so it's added to the blacklist match table.
>
> Each MIPS machine should update this table with it's compatible strings
> if it does not support i8042 controller.
>
> In order to utilize this mechanism, each MIPS machine that do not
> have i8042 controller should update the blacklist table with its
> compatible strings.
>
> Signed-off-by: Miodrag Dinic <miodrag.dinic@...tec.com>
> Signed-off-by: Goran Ferenc <goran.ferenc@...tec.com>
> Signed-off-by: Aleksandar Markovic <aleksandar.markovic@...tec.com>
> ---
>  arch/mips/kernel/setup.c       | 16 ++++++++++++++++
>  drivers/input/serio/i8042-io.h |  2 +-
>  2 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index c22cde8..c3e0d2b 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -79,6 +79,15 @@ const unsigned long mips_io_port_base = -1;
>  EXPORT_SYMBOL(mips_io_port_base);
>
>  /*
> + * Here we blacklist all MIPS boards which do not have i8042 controller
> + */
> +static const struct of_device_id i8042_blacklist_of_match[] = {
> +       { .compatible = "mti,ranchu", },
> +       {},
> +};
> +#define I8042_DATA_REG 0x60
> +
> +/*
>   * Check for existence of legacy devices
>   *
>   * Some drivers may try to probe some I/O ports which can lead to
> @@ -90,9 +99,16 @@ EXPORT_SYMBOL(mips_io_port_base);
>   */
>  int check_legacy_ioport(unsigned long base_port)
>  {
> +       struct device_node *np;
>         int ret = 0;
>
>         switch (base_port) {
> +       case I8042_DATA_REG:
> +               np = of_find_matching_node(NULL, i8042_blacklist_of_match);
> +               if (np)
> +                       ret = -ENODEV;
> +               of_node_put(np);
> +               break;

Wouldn't it make more sense to require boards to describe their i8042
device(s) in device tree if USE_OF is enabled? And maybe a whitelist
for those preexisting ones that don't. Much less maintenance overhead
for new boards, as I suspect the amount of boards with i8042 support
is much less than those that don't.

At least PowerPC seems to do it this way.


Regards
Jonas